1. Field of the Invention
This invention concerns a mixing screw for apparatuses for ice-cream production, in particular for apparatuses having a whipping vessel with vertical axis.
2. Description of the Prior Art
Apparatuses for handicraft production of ice-cream, comprising a whipping vessel with vertical axis under conditions of thermal exchange with the evaporator of a refrigerating circuit inside which a mixing screw is housed and is turned by a shaft coaxially protruding from the bottom of the vessel itself, are known. The mixing screw, besides performing the operation of mixing and homogenizing the mixture to be freezed, must also carry out the function of improving thermal exchange between the mixture and the cooled walls of the whipping vessel. For this purpose the known mixing screws generally comprise vanes capable of mixing the mixture to be freezed in the whipping vessel and of scraping off the cooled mixture from the walls in order that new mixture continuously comes into contact with the walls themselves. The two functions are generally performed by a single type of mixing-scraping vane, but it is also possible to have one or more vanes with only a mixing function. The scraping vanes have the inconvenience that their edges rapidly wear out, due to their continuous action of scraping on the bottom and on the side wall of the vessel, and said wear limits their duration, so that, after a certain time of use, it is necessary to substitute the same, with considerable incidence on maintenance costs.